The present disclosure relates to a vehicle control device, and more particularly to a vehicle control device that achieves a desired vehicle attitude (vehicle behavior) by performing an engine control.
Conventionally, devices which control the behavior of a vehicle to a safer direction when the behavior of the vehicle becomes unstable due to a slip, etc. (such as an antiskid brake system (ABS)), are known. For example, devices which detect that a behavior such as understeering or oversteering occurs with the vehicle during cornering, etc. of the vehicle, and apply a suitable deceleration to the wheels so that the behavior is controlled, are known.
Meanwhile, a vehicle movement controller is known, that adjusts a deceleration during cornering to control loads applied to front wheels which are steerable wheels so that a series of operations by a vehicle driver (breaking, steering-in, accelerating, steering-back, etc.) during cornering of a vehicle in a normal traveling state become natural and stable, unlike the above control executed for a safety improvement in the traveling state where the behavior of the vehicle becomes unstable.
Further, JP2014-166014A discloses a behavior control device for a vehicle which reduces a driving force (torque) of the vehicle according to a yaw-rate related amount corresponding to a steering operation by a vehicle driver (e.g., yaw acceleration) to quickly decelerate the vehicle when the driver starts the steering operation (vehicle attitude control) so that a sufficient load is quickly applied to front wheels which are steerable wheels. According to this behavior control device, a frictional force between the front wheels and a road surface increases and a cornering force of the front wheels increases by quickly applying the loads to the front wheels when the steering operation is started. Therefore, turnability of the vehicle in an early stage of curve entry improves, and a response to the steering-in operation (steering stability) improves. Thus, a vehicle behavior intended by the driver is achieved.
Incidentally, driving force transmission mechanisms that transmit a driving force of a vehicle to vehicle wheels are conventionally provided with various kinds of engageable elements, and change an engagement state of each engageable element according to an operating state of the vehicle (engagement state change control). If this engagement state change control and the vehicle attitude control, such as that described in JP2014-166014A, are simultaneously executed, the following problem may occur. That is, if the engagement state of the engageable element is changed by the engagement state change control while the driving force of the vehicle is reduced by the vehicle attitude control, the torque cannot be reduced sufficiently to control the vehicle attitude and a desired vehicle attitude may not be achieved. In other words, the steering stability may not suitably be improved. On the other hand, if the driving force of the vehicle is reduced by the vehicle attitude control while the engagement state of the engageable element is changed by the engagement state change control, the engagement states may not be changed quickly or stably.
Here, a situation where the driving force transmission mechanism includes a torque converter provided with a lockup clutch and the engageable element is the lockup clutch is described as one example. The engagement state of the lockup clutch is preferably in a fully engaged state when considering fuel consumption efficiency, while, in a situation or an operating range in which acceleration performance improvement, vibration reduction, etc. are required, the engagement state is preferably in a slip state or a fully released state. Therefore, the engagement state of the lockup clutch is generally controlled according to the operating state of the vehicle, such as an accelerator opening, a vehicle speed, etc. Here, if the engagement state of the lockup clutch is changed (particularly, the engagement state is loosened) due to a change in the operating state while the vehicle attitude control is executed, sufficient torque reduction for the vehicle attitude control cannot be performed and the desired vehicle attitude cannot be achieved. On the other hand, if the vehicle attitude control is executed while the engagement state of the lockup clutch is changed due to the change in the operating state, fuel consumption reduction, acceleration performance improvement, vibration reduction, etc. cannot suitably be achieved.